The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
1 Swelling around a tooth or swelling of the jaw or cheek. 2  Injury or trauma to the area.  These signs and symptoms may sometimes be associated with dental decay or gum disease (periodontal disease). Dental decay or an area of redness around the tooth's gum line may point to the source of pain.